OK, let's work through this together. We're starting with 509 and we're going to multiply it by 78, which means we add 509 to itself 78 times.
Step 1: 0 + 509 = 509
Step 2: 509 + 509 = 1018
Step 3: 1018 + 509 = 1527
Step 4: 1527 + 509 = 2036
Step 5: 2036 + 509 = 2545
Step 6: 2545 + 509 = 3054
Step 7: 3054 + 509 = 3563
Step 8: 3563 + 509 = 4072
Step 9: 4072 + 509 = 4581
Step 10: 4581 + 509 = 5090
Step 11: 5090 + 509 = 5599
Step 12: 5599 + 509 = 6108
Step 13: 6108 + 509 = 6617
Step 14: 6617 + 509 = 7126
Step 15: 7126 + 509 = 7635
Step 16: 7635 + 509 = 8144
Step 17: 8144 + 509 = 8653
Step 18: 8653 + 509 = 9162
Step 19: 9162 + 509 = 9671
Step 20: 9671 + 509 = 10180
Step 21: 10180 + 509 = 10689
Step 22: 10689 + 509 = 11198
Step 23: 11198 + 509 = 11707
Step 24: 11707 + 509 = 12216
Step 25: 12216 + 509 = 12725
Step 26: 12725 + 509 = 13234
Step 27: 13234 + 509 = 13743
Step 28: 13743 + 509 = 14252
Step 29: 14252 + 509 = 14761
Step 30: 14761 + 509 = 15270
Step 31: 15270 + 509 = 15779
Step 32: 15779 + 509 = 16288
Step 33: 16288 + 509 = 16797
Step 34: 16797 + 509 = 17306
Step 35: 17306 + 509 = 17815
Step 36: 17815 + 509 = 18324
Step 37: 18324 + 509 = 18833
Step 38: 18833 + 509 = 19342
Step 39: 19342 + 509 = 19851
Step 40: 19851 + 509 = 20360
Step 41: 20360 + 509 = 20869
Step 42: 20869 + 509 = 21378
Step 43: 21378 + 509 = 21887
Step 44: 21887 + 509 = 22396
Step 45: 22396 + 509 = 22905
Step 46: 22905 + 509 = 23414
Step 47: 23414 + 509 = 23923
Step 48: 23923 + 509 = 24432
Step 49: 24432 + 509 = 24941
Step 50: 24941 + 509 = 25450
Step 51: 25450 + 509 = 25959
Step 52: 25959 + 509 = 26468
Step 53: 26468 + 509 = 26977
Step 54: 26977 + 509 = 27486
Step 55: 27486 + 509 = 27995
Step 56: 27995 + 509 = 28504
Step 57: 28504 + 509 = 29013
Step 58: 29013 + 509 = 29522
Step 59: 29522 + 509 = 30031
Step 60: 30031 + 509 = 30540
Step 61: 30540 + 509 = 31049
Step 62: 31049 + 509 = 31558
Step 63: 31558 + 509 = 32067
Step 64: 32067 + 509 = 32576
Step 65: 32576 + 509 = 33085
Step 66: 33085 + 509 = 33594
Step 67: 33594 + 509 = 34103
Step 68: 34103 + 509 = 34612
Step 69: 34612 + 509 = 35121
Step 70: 35121 + 509 = 35630
Step 71: 35630 + 509 = 36139
Step 72: 36139 + 509 = 36648
Step 73: 36648 + 509 = 37157
Step 74: 37157 + 509 = 37666
Step 75: 37666 + 509 = 38175
Step 76: 38175 + 509 = 38684
Step 77: 38684 + 509 = 39193
Step 78: 39193 + 509 = 39702

So, 509*78 = 39702